Autostereoscopic image display systems are known in various forms of implementation, and are aimed at the recreation of the two different perspectives of a three-dimensional view or image as perceived by two human eyes without the need for viewing aids to be worn by the observer. A viewpoint tracker is used to dynamically align the point of recreation with the viewpoint or observer position, as described in, for example International Patent Application No. WO03/013153. The two different perspectives of a three-dimensional view, also referred to as a stereoscopic pair of images, allow the brain to assess the distance to various objects in a scene and to provide for three-dimensional view impression.
During a medical intervention, such as ultrasound-guided interventions, a surgeon would be watching three-dimensional ultrasound data, rendered for at least two views. It is advantageous to align the above-mentioned point of recreation, i.e. the plane where the two (or more) views intersect, with the plane on which the surgeon's eyes are focused. During a medical intervention, this will tend to be the instrument being manipulated.